Group of 20 members are world leaders, but they do not necessarily represent the world's biggest economies.
Thirteen non-member countries rank higher based on gross domestic product than G-20 participant South Africa, which ranks 32nd, according to the International Monetary Fund.
Based on purchasing power rankings, Iran, Taiwan and Thailand finish higher than South Africa without making the G-20 membership list.
G-20 nations explain the exclusion by saying that membership depends on geographical balance and population, as well as economic significance. An earlier, more inclusive group had included 33 countries but it was deemed unwieldy.
Membership in the G-20 has not changed since it formed in 1999. Members represent 85 percent of the world's economy and two-thirds of its population.
Sept. 25, 1999: The Group of 20 is formed by members of the Group of Seven industrialized nations, recognizing the growing influence of non-member countries.
Dec. 15, 1999: G-20 finance ministers and central bank governors meet for the first time in Berlin. The group represents the European Union and 19 countries: Argentina, Australia, Brazil, Canada, China, France, Germany, India, Indonesia, Italy, Japan, Mexico, Russia, Saudi Arabia, South Africa, South Korea, Turkey, the United Kingdom and the United States.
Oct. 24, 2000: In Montreal, finance ministers say they want to make the international financial system "less prone to crises."
Nov. 16, 2001: Two months after the Sept. 11, 2001, terrorist attacks, finance ministers meeting in Ottawa pledge to block terrorists from accessing international banking systems and to work at stabilizing world economies.
Nov. 22, 2002: Finance ministers meeting in New Delhi focus on globalization; crisis prevention and resolution; development and aid; and, combatting the financing of terror.
Oct. 26, 2003: In Morelia, Mexico, finance ministers say, "While risks remain, a global economic recovery is underway. ..."
Nov. 20, 2004: Finance ministers meeting in Berlin discuss demographic challenges and migration while welcoming "high growth at low inflation rates. …